Summary of Significant Accounting Policies (Direct Premium Attributable By Segment) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Annual direct premiums written	$ 2,853,169	$ 2,737,472	$ 2,655,720
Private Passenger Automobile [Member]
Segment Reporting Information [Line Items]
Annual direct premiums written	2,223,073	2,165,557	2,140,531
Homeowners [Member]
Segment Reporting Information [Line Items]
Annual direct premiums written	374,436	340,013	318,295
Commercial Automobile [Member]
Segment Reporting Information [Line Items]
Annual direct premiums written	135,928	104,689	74,655
Other Lines [Member]
Segment Reporting Information [Line Items]
Annual direct premiums written	$ 119,732	$ 127,213	$ 122,239